1. Field of the Invention
The present invention relates to drug formulation of hydrophobic photosensitizer. In particular, the invention relates to nanoparticle formulations containing hydrophobic photosensitizers, to their method of preparation and to their use in photodynamic therapy for destruction of unwanted cells or tissues, and more particularly for photodynamic tumor therapy, using intravenous administration.
2. Invention Disclosure Statement
Photodynamic therapy (PDT) is one of the most promising new techniques now being explored for use in a variety of medical applications and particularly is a well-recognized treatment for the destruction of tumors. Photodynamic therapy uses light and a photosensitizer (a dye) to achieve its desired medical effect. A large number of naturally occurring and synthetic dyes have been evaluated as potential photosensitizers for photodynamic therapy. Perhaps the most widely studied class of photosensitizers are the tetrapyrrolic macrocyclic compounds. Among them, especially porphyrins and chlorins have been tested for their PDT efficacy.
Porphyrins are macrocyclic compounds with bridges of one carbon atom joining pyrroles to form a characteristic tetrapyrrole ring structure. There are many different classes of porphyrin derivatives including those containing dihydro-pyrrole units. Chlorins and bacteriochlorins are porphyrin derivative, which contain one dihydro- or two dihydro-pyrrole units respectively.
Chlorins have their absorption spectrum in the red and near-infrared region of the electromagnetic spectrum. As light of longer wavelength penetrates deeper into the tissue it is possible to treat more expanded and deeper tumors, if the PDT is employed for tumor therapy. Chlorins can either be derived from natural sources or from total synthesis.
Chlorins from natural compounds are obtained by derivatizing chlorophylls or bacteriochlorophylls. Methods to prepare chlorins and bacteriochlorins by total synthesis generally use porphyrins, and then are converted to a chlorin or bacteriochlorin system. This conversion step can e.g. be performed by the reduction with in situ generated diimine or by dihydroxylation leading to dihydro- or dihydroxy-substituted chlorins or bacteriochlorins, respectively
Raymond Bonnett et al., in their patent No. EP 00337601B1, disclose a method for preparation of photosensitizers by reduction of corresponding porphyrins. Total synthesis of temoporfin (chemical name: (m-tetrahydroxyphenyl-chlorin))-a chlorin, is disclosed. Temoporfin (Foscan®) is successfully used in Europe as a photosensitizer for the PDT treatment of head and neck cancer. Similarly patent application WO 09613504A1 by David Dolphin et al. and patent application WO 00061584A1 by Jill Maclpine et al. teach reduction method of preparation of novel photosensitizer having improved properties.
Porphyrins can be either directly used as photosensitizers for PDT or as a precursors for the synthesis of chlorins by subjecting pyrrole and aldehyde(s) to a condensation reaction. Suitable methods for this condensation have long been known in the art.
The use of PDT for the treatment of various types of disease has been limited due to the inherent features of photosensitizers (PS). These include their high cost, extended retention in the host organism, substantial skin phototoxicity, low solubility in physiological solutions reducing their usefulness for intravascular administration thus leading to thromboembolic accidents, and lower targeting effectiveness. These disadvantages, particularly of PS in the prior art, had led to the administration of very high doses of a photosensitizer, which dramatically increase the possibility of accumulation of the photosensitizer in normal tissues and the accompanying risk of affecting normal sites.
Efforts to reduce cost and to decrease background toxicity have been underway but are unrelated to the developments of the present invention. Work to improve solubility in physiological solutions, effects of skin photo-toxicity, retention in host organism and to a lesser extent targeting effectiveness are the areas where the present invention provides new and non-obvious improvements on the use of PDT to treat various neoplasia, hyperplasia and related diseases.
Most substances successfully employed for photodynamic tumor therapy are lipophilic substances, which due to their inherent low solubility in water need to be formulated in a proper way. Therefore, there is a great need for new formulations of tetrapyrrole-based photosensitizers to enhance their uptake in the body and their bioavailability.
Nanoparticles are intensively investigated as carriers for lipophilic drug substances (N. P. Preatorius, T. K. Mandal, Engineered Nanoparticles in Cancer Therapy, Recent Patents on Drug Delivery & Formulation, 2007, 1, 37-51; M. N. V. Ravi Kumar, Engineered Nanoparticles in Cancer Therapy, J. Pharm. Pharmaceut. Sci., 2000, 3, 234-258). A nanoparticle formulation of the anti-cancer drug Paclitaxel based on human serum albumin (HSA) has been approved by regulatory authorities in Europe and the USA.
In PCT publication No. WO 01/21174 A1, Anand Burman et al. disclose a method for preparing a pharmaceutical formulation of paclitaxel an anti-cancer drug and its derivatives and analogy entrapped into nanoparticles of co-polymeric micelles. The nanoparticle is formed by a polymerization method; yet mostly polymerization reaction based method requires the use of large amount of organic solvent or unsafe stabilizer like surfactant that could results in toxic side effects.
In the prior art, nanoparticles are used for encapsulation/entrapment/adsorption of macromolecules, other therapeutic agents and diagnosing agent used for biomedical application. Majority of the nanoparticles are prepared from polymeric material, and use for their preparation large amount of organic solvents and toxic surfactants which need to be removed completely to avoid any possible side effects in patients. One of the problems that is encountered with some nanoparticulate compositions is the solubilization and subsequent recrystallization of the component crystalline drug particles. Crystal growth and particle aggregation in nanoparticulate active agent preparations are highly undesirable. The presence of large crystals in the nanoparticulate active agent composition may cause undesirable side effects, especially when the preparation is in an injectable formulation. Larger particles formed by particle aggregation and recrystallization can also interfere with blood flow, causing pulmonary embolism and death.
Nanoparticles in general are solid colloidal particles ranging in size from 10 nm to 1000 nm and are used in some drug delivery systems. Nanoparticles consist of macromolecular materials in which the active principle is dissolved, entrapped or encapsulated, and/or to which the active principle is absorbed or attached. Many different sorts of nanoparticle material have been investigated, such as quantum dots, silica-based nanoparticles, photonic crystals, liposomes, nanoparticles based on different polymers of natural and synthetic origin, and metal-based nanoparticles. Nanoparticles are diverse both in their shape and composition.
Most interesting as carrier systems for photosensitizers are nanoparticles that consist of biocompatible materials. Such carrier systems could significantly improve the treatment regimen of photodynamic therapy. A carrier system with such known high biocompatibility is e.g. human serum albumin (HSA). HSA material has successfully been formulated as nanoparticles (see. K. Langer, et al. in. Intl. J. Pharm., 2007, 347, 109-117).
There are few examples of protein-based nanoparticles as carriers for water insoluble pharmacologically active agents known in the art.
In U.S. Pat. No. 5,916,596, Desai et al. disclose a composition and method for delivery of hydrophobic anti-cancer drug paclitaxel in the form of suspended particle coated with protein. It discloses protein-based nanoparticles of size less than 200 nm diameter for drug delivery and these are sterile-filtered. Smaller size nanoparticles have greater aggregation during storage. This known art describes suspended drug particles coated with protein, which acts as a stabilizing agent, but this patent is unrelated to the present invention.
The application of a nanoparticle formulation for parenteral administration in clinical practice requires that the sterility of the formulation according to pharmacopoeial specifications can be assured. Also, for a clinical application it is desirable that the formulation can be freeze dried and later be reconstituted in an aqueous medium. Sterility of nanoparticle photosensitizer formulations involving HSA is challenging because of the lability of the nanoparticle matrix material as well as the lability of the photosensitizer. Conventional methods of sterilization (autoclaving, use of ethylene oxide, gamma-irradiation) are incompatible with the present invention photosensitizer formulations (see. K. A. Athanasiou, et al. in, Biomaterials, 1996, 17, 93-102; C. Volland, et al., J. Contr. Rel., 1994, 31, 293-305).
Eric Allemann et al. in their patent application WO 03097096A1 disclose compositions and methods for parenteral or local delivery of photosensitizer using bridgeable nanoparticles containing polyester polymers. It also discloses preparation and use of such nanoparticles. The nanoparticles are sterilized using filtration methods. Nevertheless, this method has its drawbacks and is not generally compatible with the nanoparticles that are subject of the present invention. Pore size for sterile filtration is usually no greater than 0.22 μm (≧220 nm) whereas nanoparticles of the present invention populate essentially the whole size range between 100 and 500 nm. Therefore, sterile filtration has its drawbacks and is generally incompatible with the nanoparticles that are subject of the present invention.
In particular, it is difficult to develop sterile nanoparticle formulations and nanoparticle formulations suitable for freeze drying in the case of photosensitizers of the present invention which are of the chlorin or bacteriochlorin type (i.e. tetrapyrroles carrying one or two dihydro-pyrrole units), because such systems are especially sensitive to oxidation and photo-chemical modifications induced by the handling conditions that are often used for nanoparticle preparation (Y. Hongying, et al. Dyes Pigm. 1999, 43, 109-117; C. Hadjur, at al., J. Photochem. Photobiol. B: Biology, 1998, 45, 170-178; R. Bonnett, et al. in J. Chem. Soc. Perkin Trans. 2, 1999, 325-328). These photosensitizers of the chlorin or bacteriochlorin type which possess one or two dihydro-pyrrole units, respectively, differ significantly in their chemical and physical behaviour from their corresponding porphyrins (R. Bonnett, et al. in J. Chem. Soc. Perkin Trans. 2, 1999, 325-328; R. Bonnett, et al. J. Porphyrins Phthalocyanines, 2001, 5, 652-661).
The known prior art on HSA-based nanoparticles used as carriers for photosensitizers does not address problems related to sterility and freeze-drying of HSA-based nanoparticles and the investigated photosensitizers are less problematic in this respect because of their more stable chemical structure.
Hydrophobic photosensitizers need to be formulated using suitable carriers due to their inherent low solubility in water. Therefore, there is a great need for new formulations of tetrapyrrole-based photosensitizers to enhance their uptake in the body and their bioavailability. The use of PDT for the treatment of various types of disease has been limited due to the inherent features of photosensitizers (PS). These include their high cost, extended retention in the host organism, substantial skin phototoxicity, low solubility in physiological solutions reducing their usefulness for intravascular administration thus leading to thromboembolic accidents, and lower targeting effectiveness.
The present invention obviates the above discussed problems seen in the formulation of hydrophobic photosensitizers by providing a pharmaceutical compatible nanoparticle made of natural material as a drug delivery system and for parenteral administration. Present invention also provides method to improve the bioavailability, stability and solubility of sensitive hydrophobic PS.